1. Field of the Invention
The present invention relates generally to satellite based communications, and in particular, to a method, apparatus, and article of manufacture for conducting high bandwidth optical communication between a satellite and a ground station.
2. Description of the Related Art
Low earth orbit (LEO) satellites are commonly used for a variety of tasks including earth observation, spy satellites, conducting experiments (e.g. on the International Space Station), etc. Ground-to-space communication with such satellites is crucial. High-speed free-space optical (FSO) laser communications have been used for ground-to-space links. Optical wireless free space communications involving moving parties (e.g., satellites), especially at extra-long distances, require precise beam pointing and tracking.
To transmit data to a satellite, ground stations commonly transmit an optical beam to a satellite (whose location may be known based on ephemeris data). To transmit data from the satellite to the ground station, the satellite steers an optical beam down to the ground station using opto-mechanical methods (e.g., a gimbal). However, beam steering using diffractive elements including liquid crystal (LC) arrays, MEMs (micro-electro-mechanical) arrays, electro-wetting arrays, or any other grating elements suffer many drawbacks. For example, the grating efficiency drops as the scan angle increases which inherently limits all of the above approaches to small angle scanners and therefore necessitates complicated multi-stage designs. Further, the above approaches do not realize sufficient control over light. In this regard, the above approaches are inherently mechanical and therefore impose vibration and inertia design challenges, while also providing only limited control over optical phase. In view of the above, what is needed is a method for establishing satellite-to-ground communications that do not rely on opto-mechanical methods and eliminate the drawbacks set forth above.